Smelting apparatus and method



Nov. 4, 1958 Filed Jan. 28. 1954 J. B. BRENNAN 4 Sheets-Sheet 1 fa 19 j INVENTOR.

' J05fP/1 a. MINA AM ATTOENEXi.

Nov. 4, 1958 I J. B. BRENNAN 2,858,586

SMELTING APPARATUS AND METHOD Filed. Jan. 28, 1954 I 4 Sheets-Sheet 3 m I I g E: 74 4 4/ T: I x 4.6

INVENTOR. I J05Pfl B. ZlPf/V/VAN MMMJ Nov. 4, 1958 J. B. BFAENNAN 2,853,535

SMELTING APPARATUS AND METHOD Filed Jan. 28. 1954 4 Sheet s-Sheet 4 JNVENTOR. JOJEPHAB. ZRf/VA/AA/ AT TOQVEX5.

United States Patent SMELTING APPARATUS AND METHOD Joseph B. Brennan, Cleveland, Ohio Application January 28, 1954, Serial No. 406,809

7 Claims. (Cl. 22-572) The present invention relates generally as indicated to a smelting apparatus and method, and more particularly to such apparatus and method applicable in the melting of titanium or like metal and alloys thereof.

A primary object of this invention is to provide an apparatus having a chilled crucible which maintains a skin or skull of metal thereagainst to prevent reaction between the metal and the crucible and to prevent contamination and which has reflector-type heating elements focused on the metal in the crucible to maintain the same in molten condition within such skull, the molten metal being drawn off from the crucible for continuous casting or for casting into molds.

The method, accordingly, as stated in the foregoing principal object of this invention, consists in forming a skin or skull around a pool of molten metal while heating the pool to maintain the metal in molten condition for cast- 1ng.

Another object of this invention is to provide a vacuum apparatus and method wherein the smelting is accomplished in a partial vacuum or, if desired, in a controlled neutral or non-oxidizing atmosphere.

Another object of this invention is to provide an apparatus and method wherein metal in solid form, for example in bar or rod form, slug or chunk form, consolidated powdered, and sintered form, or powdered or granule form, is introduced into the apparatus for melting and collection as a pool, the outside of the pool being solidified to form a skull and the main body of the pool, especially at the center thereof, being heated by reflectortype heaters to maintain the metal in molten condition for casting.

Another object of this invention is the overcasting of a fed-in rod or other shape of sintered metal.

Another object of this invention is to provide an apparatus and method which involves feeding in of powdered metal, consolidation of the powder into a coherent bar, and then overcasting onto said bar.

Other objects and advantages of the present invention will become apparent as the following description proceeds.

To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

In said annexed drawings:

Figs. 1 and 1A are central vertical cross-section views of contiguous portions of a continuous casting apparatus to which the present smelter supplies molten metal for casting;

Fig. 2 is a fragmentary cross-section view of a smelter like that of Fig. 1 wherein powdered or granular metal is melted;

Fig. 3 is a fragmentary cross-section view of a smelter Patented Nov. 4, 1958 similar to that of Fig. 4 except designed to accommodate metal chunks or slugs;

Fig. 4 is a central vertical cross-section view of the smelting portion of a continuous castingapparatus; and

Fig. 5 is a vertical cross-section view of a wheel-type continuous casting apparatus.

Broadly stated, when the apparatus includes a vacuum or controlled atmosphere chamber, it will include, for example, a bell jar into which metal in solid form is introduced, means for melting the metal thus introduced into the chamber, means for collecting the molten metal, means for forming a skull of solidified metal around the molten metal, and, in some instances, heating means for maintaining a fluid center wherefrom the molten metal may be continuously drawn for forming, for example, a continuous casting, individual castings in a cluster, or individual castings in molds which are successively positioned in communication with the fluid center of the pool.

Accordingly, broadly stated, the method consists in melting metal, solidifying a skull of metal on the body of the fluid metal, heating the metal within the skull, and discharging the molten metal from the fluid center in either a continuous or an intermittent manner.

Referring now more specifically to the drawings, the apparatus shown in Fig. 1 comprises a housing 1 in the form of a bell jar mounted on a closure member 2 and provided with a vacuum or controlled atmosphere connection 3 whereby the chamber 4 within said housing may be evacuated or supplied with a desired neutral or non-oxidizing atmosphere.

The upper end of said housing 1 is formed with an opening, around which is a suitable packing ring such as an O-ring 5 cooled by circulation of coolant through cored passage 6. Solid metal rod or bar or sintered metal bar 7 is adapted to be shoved down through the opening in housing 1 in sealed engagement with the packing ring 5 thereat, and as the metal is moved down through the high frequency heating coil 8 (which is preferably a surface melting coil operated at 400 kc. or over for titanium), the lower end thereof is melted. Beneath the lower end of the thus downwardly moved metal 7 is a chilling crucible 9 and a chilling mold 10, each being cooled by circulation of water or other coolant fluid therethrough; the latter, that is, the mold 10, having a passage 11 therethrough of the cross-section shape and size of the continuous casting 12 to be produced.

In starting the apparatus, a previously cast bar or plug is shoved upwardly through the passage 11 up almost to about the bottom of the crucible 9. Thus, molten metal melted by the high frequency coil 8 will collect as a pool 14 in said crucible; and, of course, the circulation of cooling medium through said crucible 59 will cool the wall thereof so as to form a crust or skull 15 on said pool of molten metal and thus prevent reaction between the molten metal and the crucible.

For the purpose of maintaining the center of the skull in molten condition, reflector-type focused heaters 16 are employed, each consisting of a block of graphite or the like having a parabolic heat-radiating surface 17 focused on the central portion of the pool 14, said blocks being heated by means of high frequency coils 18 therearound.

The plug or bar 12 inserted upwardly through passage 11 is then moved downwardlyat a uniform lineal speed as by suitable drive rollers 19 or the like, whereupon the molten metal 14 in the crucible 9 will flow down therewith into the axial center of and partway through the mold 10, said mold being cooled as by constant circulation of coolant such as water therethrough so that a skin will be formed immediately on the casting 12 to prevent reaction between the metal and the mold passage 11.

As the casting 12 is thus being continuously withdrawn from passage 11, metal is being added into pool 14' at substantially the same rate by the high frequency coil 8. It is, of course, to be understood that the high frequency coil 8 may be omitted and melting accomplished by focusing the reflector-type heaters 16 not only on the central portion of the pool 14, but also on the lower end portion of the metal 7 introduced into the housing 1 through the top opening thereof.

In order to insure uniform heating of the metal in the pool 14 and in order to prevent the formation of channels or grooves, it is preferred to make the crucible 9 of a twopart construction with the bowl or dish part 20 thereof rotatable at a uniform speed as by drive pinion 21 engaged therewith. Also the reflector-type heaters 16 may be mounted, if desired, for uniform oscillation and/or rotation to uniformly distribute the heating effect thereof on the molten metal in the pool 14. Or the reflectors 16 may be an annular ring having an inner reflecting surface focusing on the central portion of the skull 15 so that the molten metal is heated and kept fluid as it descends through the center of the skull 15 as fast as it is melted and when melted on the end of the feed bar 7 by the coil 8 and on heaters 16.

As the casting 12 emerges from the lower end of passage 11, sealed by a packing ring if desired, it passes through another vacuum or desired atmosphere chamber 23 having a vacuum connection 24.

Instead of casting through a mold 10 as shown in Fig. 1, it is also possible to form a continuous casting by casting onto the groove or grooves of a chilled rotary wheel.

As a further alternative, the smelting apparatus herein disclosed may be used in conjunction with casting operations wherein a series of molds are shoved through casting and chilling zones as disclosed, for example, in my copending application Ser. No. 202,707, filed December 16, 1950. It is also possible to melt powdered or granular metal or slugs of metal in the present apparatus, using the principle disclosed in my copending application Ser. No. 393,123, filed November 19, 1953, wherein slugs of metal are introduced into the housing from a rotary indexing feed table for melting, and the melted metal is introduced into molds carried as by means of a rotary indexing work table.

The casting may be done also into a cluster-type breakable mold having a series of radiating cavities, the molten metal being fed from the central portion of a chilled crucible through passages in the mold to the respective cavities.

It was previously indicated that the metal 7 to be smelted may be in solid form or sintered form, preferably the latter, when introduced into chamber 4. In order to continuously produce and to feed such metal 7, it is preferred to employ apparatus such as is disclosed in my copending application Ser. No. 318,617, filed November 4, 1952. In the modified form thereof, as shown herein, the exit end is defined by a housing 25 having a vacuum connection 26 to thus form a vacuum chamber 27 through which said sintered or solid metal 7 passes, there being a fluid-cooled packing ring 28 around the top opening of said housing 25.

Instead of employing a reciprocating plunger as in Ser. No. 318,617, a reciprocating rotary feed screw 30 may be employed to compress or compact the 200 mesh metal powder 31 in the cylinder 32. Metal powder 31 is supplied into cylinder 32 as from a feed hopper 34 which may be equipped, if desired, with a closure lid 35 and a vacuum connection 36. The wall of said cylinder 32 has a vacuum connection 37 covered by a filter plate 38 to prevent vacuum withdrawal of the metal powder. The pressed powder in cylinder 32 then passes through the field of a high frequency coil 39 effect to vacuum sinter the metal powder (or to melt the same, if desired), and finally through a fluid cooled die 40which effects solidification of the sintered or melted metal powder.

Alternatively, a fused skin only may be effected on the advancing powder cylinder.

Inasmuch as the casting 12 has been formed by chilling the exterior thereof, the same may have surface irregularities which are eliminated by surface fusing by means of high frequency coil 41 in the aforesaid chamber 23 and then passing the same between fluid cooled rollers 19.

Below said rollers 19 is another casting crucible 42 heated by coil 43 and having a fluid-cooled die 45 and a fluid seal 46. Previously evacuated or degassed molten metal 47 such as steel, copper, or aluminum is supplied to crucible 42 as through conduit 48, and as the casting 12 passes through die 45 a thin outside skin of such metal will be cast thereagainst; and as the coated casting passes through the fluid cooled die 45 and then through the fluid seal 46, which may be aluminum, for example, when the coating is steel or copper, or lead or the like when the coating material is aluminum, the completed coated casting issues from the bottom of the apparatus and passes through another fluid cooled O-ring 49 and then may pass through another set of drive rolls 19 (not shown). The overcast skin of metal 47 protects the casting 12 from oxidation and is especially desirable in the casting of the group IV metals of the periodic chart for subsequent hot-rolling because of contamination otherwise encountered. The smooth outside skin also enables the maintaining of a vacuum seal of chambers 23 and 4 because it is slick.

Fig. 2 shows an embodiment of the invention wherein a rotary indexing feed table 50 has openings 51 therethrough which are adapted to be filled with powdered or granular metal 52 as the successive openings pause under the feed funnel 53. When the table 50 is indexed to position a filled opening 51 in register with the opening 54 of housing 56, the contents 52 thereof will drop down into pool 14 for melting. The housing 56 will otherwise correspond to housing lin Fig. 1 having reflector heaters 16 focused on the center of the pool 14 or skull 15.

The apparatus of Fig.2 may be employed in supplying slugs or chunks of metal 57 from openings 51 into a crucible 58 for melting as shown in Fig. 3, the chunks 57 being promptly melted by high frequency coil 59, the molten metal running down into the crucible 9 therebeneath.

As before mentioned, the present apparatus and method has particularly utility in the casting of titanium and its allows and also the other metals in group IV of the periodic table. Heretofore, the only known method of melting titanium so as to provide a fluid center and a solid skull against a water-cooled jacket has been to employ an electric are either using a titanium electrode combined with graphite, tungsten, carbon, or like electrodes, this being a rather costly proposition and apt to result in a contamination of the titanium with consequent embrittlement as well as other known difficulties.

One difiiculty with the casting of titanium is that, in a vacuum, the molten metal reacts vigorously with certain refractory oxides such as aluminum oxide, for example, and therefore it is not possible to have a prolonged contact of the molten metal with a crucible or with a mold formed of any such refractory oxide. However, at sintering temperatures under vacuum, mold reaction is acceptable.

As apparent from the foregoing descriptions of Figs. 1 to 3, the main feature of the invention is the introduction of solid metal in powdered, granular, slug, chunk, rod, or bar form into a vacuum or other desired atmosphere chamber for melting and collection in a pool, the outside of which pool is chilled to provide a crust or skull which eliminates reaction between the metal and the container or crucible therefor. In addition, the central portion of the pool is maintained in molten condition for casting therefrom as by means of reflector-type heaters focused on the central portion of the pool. As

before, the high frequency melting of the solid metal may be dispensed with, in which case the reflector-type heaters will be focused not only on the pool but also on the lower end portion of the metal introduced for melting.

Also the reflector-type heaters 16 may be dispensed with if enough energy is used on the coil 8, Fig. 1. The skull and crucible 9 may be dispensed with if one is satisfied with the production of coil 8, and molten metal drops clear of the walls of the tube 11 and in the center only thereof.

The containers or crucibles for forming such skull on the pool of molten metal therein may be made of copper, for example, cooled as by circulation of water or other suitable coolant. Similarly, the molds for continuous casting as in Fig. 1 will be in the form of Water-cooled copper jackets to effect instantaneous solidification of the out-er shell of the cast metal as the same flows or drips through and into the mold passage.

As a specific example of the Fig. 1 apparatus for continuous casting of titanium bar 12, say of cylindrical cross-section shape and of about 4" diameter, the chamber 4 and also chamber 24 will be maintained under a vacuum of less than 25 microns. The titanium bar 7 to be smelted may be of 2" diameter and is adapted to be shoved down at the rate of about 6" per minute through an ll-turn high frequency coil 8 operating at /2 megacycle and having a generally tapered formation of which the smallest turn is about 1" diameter and the largest diameter turn of about 3" diameter. Said coil 8 is in this instance of about 6" in length vertically from the smallest turn to the largest turn.

The reflector-type heaters 16 may be in the form of graphite blocks of about 5" diameter having coiled therearound 9600 cycle high frequency heating coils 18 to heat said blocks 16 to a temperature of about 2300 C., the heat being focused on the central portion of the pool 14 of the molten titanium. In this case, 8 such reflectortype heaters 16 are uniformly spaced and disposed at an angle of about 60 and 10" away from the top surface of the pool.

The copper jacket 20 of the crucible 9 may be of about /s" thickness, and by circulating water at 20 C. and at a pressure of 70 p. s. i. through the crucible 9, a skull of about 1 to 2" thickness is formed on the metal 14 when the titanium bar 7 is being melted at the rate of 6" per minute, and the casting 12 is withdrawn at a rate corresponding to the volume of metal thus melted per minute.

The mold 110 is hollow as shown and is adapted to have water at C. and at a pressure of 70 p. s. i. circulated therethrough, the passage 11 being approximately 6 to 10" long and the wall thereof of copper approximately 4;" in thickness. As the casting 12 is withdrawn at the rate of melting of bar 7, the titanium is progressively solidified from the outside toward the inside, and at the time that said casting 12 emerges from the lower end of said mold 10, the entire cross-section is solidified at a temperature less than the freezing point of the titanium. The casting 12 thus issuing from the mold passes through the vacuum chamber 23 while the same is yet in a heated state.

The surface fusing by the A2 megacycle or higher frequency coil 41 is only about A2 in depth, and immediately thereafter the casting passes between rolls 19 and thence through coating metal in crucible 42 for application of a skull of A to thickness in die 45. The casting 12 as it issues from the lower end of the apparatus shown in Fig. 1A may then be cut into desired lengths or else may be subjected to other operations such as rolling, forging, etc.

In the case of the Fig. 2 apparatus, powdered or granular titanium is intermittently fed into the pool 14 so as to maintain an approximately constant volume of molten metal in said pool as the casting operation progresses. The powder or granules 52 drop down directly into the pool 14, in which case the reflector-type heaters 16 will melt the same and also provide a molten central pool portion from which metal is drawn for the casting operation while a skull 15 is maintained on the pool to prevent reaction between the titanium and the crucible 9. It is preferred that the down feed from the pool not touch the wells 11 but drop in center of bar 12.

The apparatus shown in Fig. 3 is, as aforesaid, generally similar to that in Fig. 2 except that, instead of introducing powder or granules of metal into the vacuum chamber, slugs or chunks of metal 57 are introduced into the vacuum chamber for melting by the high frequency coil 59 which, like coil 8, is operated at /z megacycle or higher frequency to effect melting of the slugs 57 at approximately the same rate as the melting of the bar or rod or sticks 7.

With reference to melting of a rod or bar as it is continuously advanced through a tapered coil high frequency field, reference should be made to my Patent No. 2,648,567, granted August 11, 1953.

Referring further to the reflector-type heaters 16, these may be made of graphite or carbon as aforesaid, and in some instances, it may be desirable to provide thereon a coating of a metal or metallic oxide such as, for example, ZrO or tungsten or a metallic carbide such as tungsten carbide or titanium carbide for the purpose of preventing a reaction and also for improving the reflectivity focusing thereof.

The melting of the metal introduced into the chamber of the apparatus may also be accomplished as by means of infra-red ray types of heating apparatuses which are concentrated or focused on selected areas of the pool 14 or/ and the end of the fed-in bar. In cases where molds are shoved down through a pool and cooling guide, said heaters 16 or the equivalent thereof may be focused or concentrated in annular or ring-shape form at a portion of the pool surrounding the molds shoved down through the pool.

A vacuum compacted shape made as in my aforesaid Ser. No. 318,617 may be fed into vacuum chamber 4 as in Fig. 1, but notmelted. It can be fed down through said vacuum chamber after being cooled and then through a surrounding surface fusing coil operating, for example, at 400 kc. or over and through a cooling chamber and die and then overcastwith steel or other metal from a surrounding pool to seal on the exit through a lower metal pool as in lower portion of Fig. 1. A fused skin compacted rod of group IV metals in vacuum also may be self-quenched by the inner powder compact and will be smooth enough to seal with O-rings on exit from a vacuum chamber.

Referring now to Fig. 4, the rotating and axially reciprocating feed screw 65 around a rotary core 67 compacts and incrementally advances the metal powder 68 from feed hopper 69 through a high frequency coil 70 for sintering the metal in tubular form and then cooling the same, all under vacuum as described in connection with Fig. 1. As the lower end of the sintered, compacted tube 71 passes through the tapered high frequency coil 72, the tube is melted as shown to corresponding tapered form, the drops of molten, metal dropping down into the fluid cooled die.73 for solidification as a continuous, downwardly moving casting 74. Then follows the surface fusing and overcasting of a sealing sheath as illustrated in Fig. 1.

Although mention is made of vacuum chambers herein, it is to be understood that argon or other gas may be circulated through the chambers or held therein.

It is possible to cast a tubular shell of the metal 47, Fig. l, in vacuum and to till the same with cast metal and use a tubular shell with a sintered bar of group IV metal therein or a. casting thereof to hot roll the enclosed bar.

With. reference to Fig. 3, the crucible 58 therein is preferably made of. non-conductive ceramic material 7 such as thorium oxide or zirconium oxide highly densified and of very fine powder such as 300 mesh. This crucible, in any case, should be made of a ceramic material which is not highly reactive with the group IV metals or other metals being processed.

The high frequency coil 59 is of the water-cooled type preferably including a copper tubing disposed in spaced relation within a vicor glass or other completely fused non-conductive glass composed as of 96% fused silica for circulation of cooling water through the copper tube and there around. If desired, a copper wire may be employed. The spacing of the copper tube or wire within the glass tube allows for expansion and contraction and the glass tube prevents shorting out of the high frequency coil due to splattering of the metal under vacuum. Obviously, this type of high frequency coil 59 may be used, for example, in place of the high frequency coil 8 as shown in Fig. 1. The splattering in Fig. 1 is much less than otherwise when using vacuum compacted sintered bar.

Although the methods and apparatuses as herein disclosed refer to titanium and to the group IV metals generally, it is to be understood that the apparatuses and methods may be employed in connection with the melting and continuous casting of other metals such as chromium, cobalt, molybdenum, or alloys thereof.

The enclosure of the high frequency conductor in an impervious bar such as vicor glass tubing above referred to substantially lessens or completely avoids sintillation between turns of the coil which are due to gas ionization in vacuum.

In some instances, it may be desirable to employ resistance filaments to achieve reflected concentrated heat for the melting of either individual metal slugs or given areas or portions of the metal within the skull from which it is desired to develop a flowing stream for continuous casting or for casting into molds.

In the examples given, the time of melting in the case of titanium should be less than 30 seconds, and likewise the cooling time should be as short as possible and directional so as to improve the grain structure of the casting. Thus, for example, in Fig. 1 the cooling is effected in a direction longitudinal of the casting 12.

It is further comtemplated to form compacts or briquets from powdered titanium and to sinter the same as they are advanced downwardly through a guide tube into the melting zone. Such sintering can be carried out at a temperature of about 1000 C. and at this temperature no appreciable reaction with refractory materials is experienced. If a fused outside skin is formed on a continuously sintered powdered briquet or rod, then it may be hot-rolled very satisfactorily using the fused outside skin as a container for the enclosed powder. Furthermore, if a skin on titanium compacted rod is fused as by high frequency of 20 megacycles and the powder therein is evacuated prior thereto, a superior and less gas-contaminated product is obtained which may be hot-rolled to make sheet and rod or tubing.

The overcasting as herein disclosed for the purpose of vacuum sealing a continuous casting is of utmost importance. Such overcasting provides a protective sheath around the casting for the purpose of hot-rolling; and, of course, after hot-rolling, this sheath may be removed mechanically, or by etching or by evaporation or by other means. When the bar is vacuum sintered and has a sheath cast thereover, the evacuated sintered bar may be made into very dense sheet or rods by hot-rolling.

It is to be noted that in the several forms of the invention herein disclosed, the molten metal is fed in centrally and in line with the center .line of the casting therebelow. When a compacted exteriorly fused bar is fed through the overcasting or sheathing pool, this provides a smooth exterior surface on the bar for eflective vacuum sealing, and the overcast sheath protects the bar against oxidation when hot-rolling the same.

As previously mentioned, and as shown in Fig. 5, it is possible to form a continuous casting by casting molten metal into the groove or grooves of a chilled rotary wheel 81 or by casting onto a metal strip 82 passing around said wheel to continuously form a laminated strip 83. The metal strip 82 may be of steel, for example, and the metal 84 cast thereagainst may be some other lower melting point metal or alloy such as bronze, copper, aluminum, or the like.

As shown in Fig. 5, the crucible 85, made of graphite or other refractory material, embraces the upper portion of the wheel 81 and is formed with a molten metal discharge passage 86 which communicates with the die passage 87 defined (in the case of laminating of strip) between the metal strip 82 and the wall of the die 89 formed as an extension of crucible 85. In the case of casting of strip metal, die passage 87 will be defined between the periphery of the wheel 81 and the die wall 87 of said die 89. The wheel 81 is hollow, as shown, for circulation of cooling water or the like therethrough, and said wheel may be made of metal such as copper, for example, and the peripheral wall thereof will be relatively thin such as to permit rapid extraction of heat therethrough.

Surrounding the upper portion of the crucible is a high frequency heating coil 90 which is operative to maintain the metal 84 therein in molten condition for casting onto the wheel 81 or onto the metal strip 82 which passes around said wheel.

In the Fig. 5 embodiment, the upper portion of the wheel 81 and the strip 82 passing thereover may be heated to some extent in passing through the field of the surrounding high frequency coil 90; and, of course, in forming laminated metal strip 83, it is desired that the metal strip 82 be heated to bonding temperature at the time that the molten metal 84 is cast thereagainst. However, as soon as the metal strip 82 is contacted by the molten metal 84, the cooling effect of the wheel 81 and strip 82 will form a skull or floor on the cast metal which serves to transport the overlying molten metal through the die 89, the overlying metal having a slick or slippery surface in sliding contact with the stationary die wall 87.

As evident, the die 89 which embraces the wheel in concentric, spaced relation thereto has no appreciable heat-extracting capacity. Accordingly, the unidirectional radial cooling inwardly across the thickness of the casting or lamination results in a product which has better wearing qualities and better wetability with oil for improved lubrication when the cast product or laminated product is used as a bearing, for example. In other words, the grain growth is across the thickness of the casting, whereby the ends of the grains are subject to compressive stress in a bearing or the like.

It can be seen that, with the Fig. 5 apparatus used for casting metal strip or for forming a laminated strip as illustrated, all or substantially all of the heat of the cast metal or laminating metal 84 will be extracted through the Wheel 81 to form the skull or floor which serves to transport the overlying metal through the die. As the cooling progresses, the floor or skull finally becomes equal to the thickness of the casting or of the laminating metal, but

' until the entire cross-section has been solidified, the outer surface of the casting or laminating metal is kept in a labile state in contact with the fixed or non-movable wall 87 of the die 89. In other words, the outer surface of the casting or laminating metal is in a slippery or slick condition while in contact with the fixed die wall 87 so as to effect a smoothening of trowelling action for achieving accuracy as well as smoothness.

In connection with wheel casting, reference should be made to my copending applications Ser. No. 213,559, filed March 2, 1951, now abandoned; Ser. No. 249,525, filed October 3, 1951, now Patent No. 2,757,246, issued August 7, 1956; and Ser. No. 253,901, filed October 30, 1951, now abandoned. Apparatuses of the types disclosed in these copending applications may be used without the cooling passages or coils on the outside of the wheel and on the outside of the casting or lamination, and therefore all or substantially all of the heat of the cast metal will be extracted unidirectionally inward through the wheel for the puiposes aforesaid.

ther modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims, or the equivalent of such, be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a smelting apparatus for titanium, titanium alloys, and like metals, the combination of an enclosure, high frequency heating means for melting such metal in said enclosure for descent by gravity in particulate form, a crucible in said enclosure for collecting a pool of the thus melted and dropping metal particles, means for maintaining the pool-supporting wall of said crucible at a temperature less than the freezing point of such metal whereby to form a skull of solidified metal against such wall, and reflector-type heating means directing heat rays onto the portion of the pool Within such skull for solely maintaining the metal molten for casting without contaminating the metal.

2. In apparatus of the character described, the combination of an enclosure, means for introducing metal into said enclosure, high frequency heating means for melting such metal in said enclosure, a crucible in said enclosure for collecting a pool of melted metal, means for maintaining the pool-supporting wall of said crucible at a temperature less than the freezing point of such metal whereby to form a skull of solidified metal against such wall, reflector-type heating means directing heat rays onto the portion of the pool within such skull for solely maintaining the metal molten for casting without contamination thereof, and a mold in said enclosure and beneath said crucible into which the molten metal from within such skull is cast for solidification therein.

3. In apparatus of the character described, the combination of an enclosure, means for introducing metal into said enclosure, high frequency heating means for initially melting such metal in said enclosure, a crucible in said enclosure for collecting a pool of melted metal, means for maintaining the pool-supporting wall of said crucible at a temperature less than the freezing point of such metal whereby to form a skull of solidified metal against such wall, reflector-type heating means focusing heat rays onto the portion of the pool within such skull for solely maintaining the metal molten for casting without contamination thereof, and a chilled mold in said enclosure and beneath said crucible through which the molten metal from within such skull is continuously cast for emergence in shape-retaining form.

4. In apparatus of the character described, the con1- bination of an enclosure, means for introducing metal into said enclosure, high frequency means for initially melting such metal in said enclosure, 2. crucible in said enclosure for collecting a pool of melted metal, means for maintaining the pool-supporting wall of said crucible at a temperature less than the freezing point of such metal whereby to form a skull of solidified metal against such wall, reflector-type heating means focusing heat rays onto the portion of the pool within such skull for solely maintaining the metal molten for casting without contamination thereof, and a chilled downwardly extending mold in said enclosure and beneath said crucible through which the molten metal from within such skull is continuously cast for emergence in shape-retaining form, said crucible having an opening through the bottom thereof, and said mold having a passage therethrough of 10 desired cross-section shape and size which at its upper end registers with the opening in said crucible.

5. In apparatus of the character described, the combination of an enclosure, means for introducing metal into said enclosure, high frequency means for initially melting such metal in said enclosure, a crucible in said enclosure for collecting a pool of melted metal, means for maintaining the pool-supporting wall of said crucible at a temperature less than the freezing point of such metal whereby to form a skull of solidified metal against such wall, high frequency reflector-type heating means focusing heat rays onto the portion of the pool within such skull for solely maintaining the metal molten for casting without contamination thereof, a chilled mold in said enclosure and beneath said crucible through which the molten metal from within such skull is continuously cast for emergency in shape-retaining form, another enclosure through which the casting passes, and means for applying a protective layer of another molten metal to the casting before it emerges from said another enclosure.

6. In a continuous casting method, the steps which comprise feeding molten metal into one end of an openended chilling die and therethrough into a vacuum chamber, extracting heat from the metal as it flows through the die at a rate to solidify the metal to shape-retaining form before it emerges from the other end of the die, and, While the solidified metal is in the vacuum chamber, reheating the same to fuse only the skin thereof whereby to densify the skin thereof andto render said skin less reactive when subsequently worked.

7. The method of smelting titanium, titanium alloys, and like metals comprising the steps of introducing a solid metal into a vacuum chamber, initially melting the metal by high frequency electrical energy to avoid contamination thereof, collecting the melted metal in a pool surrounded by a skull of solidified metal, maintaining the metal molten within such skull solely by directing high frequency electrical energy thereto further to avoid contamination, and casting the molten metal Within such skull into a mold.

References Cited in the file of this patent UNITED STATES PATENTS 1,651,678 Davis Dec. 6, 1927 1,697,606 Maxson Ian. 1, 1929 1,917,461 Rankin July 11, 1933 1,956,467 Palm Apr. 24, 1934 2,055,980 Liebmann Sept. 29, 1936 2,303,873 Anderson Dec. 1, 1942 2,423,054 Strickland June 24, 1947 2,500,872 Root et al. Mar. 14, 1950 2,541,764 Herres et al Feb. 13, 1951 2,564,337 Maddex Aug. 14, 1951 2,640,792 Binder June 2, 1953 2,640,860 Herres June 2, 1953 2,676,882 Hatch Apr. 27, 1954 2,686,822 Evans et a1 Aug. 17, 1954 2,688,169 Gruber et al Sept. 7, 1954 2,709,842 Findlay June 7, 1955 2,734,244 Herres Feb. 14, 1956 FOREIGN PATENTS 844,806 Germany July 24, 1952 OTHER REFERENCES Transactions A. S. M., vol. 46, 1954, pages 270-274, inclusive. (It is noted that on page 257, it is stated that this paper was presented before the Eighth Western Metal Congress of the Society held Mar. 23 to 27, 1953.) 

